1. Field of the Invention
The present invention relates to liquid-sensitive actuators for actuating devices upon immersion in a liquid and, more particularly, to a liquid-sensitive actuator for causing a physical displacement or movement to which a device to be actuated is responsive.
2. Description of the Prior Art
Various types of liquid-sensitive actuators are described in the prior art. These are used to produce a response to the presence of a liquid. Typically, the response may be the triggering of an alarm, the starting of a pump or the deployment of an inflatable flotation device, such as a life vest, raft, or the like.
In flotation device applications, at least one inflatable envelope or cell is coupled to and inflated by carbon dioxide gas which is released from a conventional CO.sub.2 cartridge when the device is immersed in water. Typically, a piercing pin is driven forward into the sealing diaphragm at the end of the CO.sub.2 cartidge to permit the escape of gas from the cartridge through a conduit or channel into the inflatable cell. In some, the piercing pin is spring-loaded and retained in a retracted position by a water soluble element. Contact with the water dissolves the element and permits the spring to drive the piercing pin forwardly into the cartridge diaphragm. In others, a battery-activated explosive squib or charge drives the piercing pin forwardly when detonated. Some of these employ a battery which is not activated until water enters its interior, causing a chemical reaction which generates sufficient voltage and current to detonate the explosive squib. Some batteries of this type operate only in salt water. Other detonator-type devices use an immersion switch to close a circuit through the salt water itself when the switch contacts are immersed. Still others use pressure-actuated switches which close the circuit when the switch is submerged to a predetermined depth. Other devices use an expandable element expandable on contact with the water to impart displacement to a trigger. The trigger detonates an explosive squib or charge or releases a spring-load mechanism which drives a sealing pin forward into the sealing diaphram of the CO.sub.2 cartridge.
In substantially all of these flotation devices, a manual backup actuator is provided for inflating the device should the automatic features of the device fail. It has been found that most of the prior art devices have required unacceptably high reliance on the manual backup actuator because of frequent failure of the automatic system, or excessively slow reaction time to immersion. Unfortunately, failures or slow reactions of the automatic systems have resulted in numerous deaths and injuries of, for example, aviators or seamen who, due to trauma suffered during an accident or other unfortunate event, are unconscious at the time they enter the water and cannot manually actuate the flotation devices themselves. Many of the prior art devices also suffer from a high rate of premature actuation and deployment due to undesirably high sensitivity to ambient humidity. Premature actuation can often dangerously interfere with critical tasks being performed by personnel wearing these devices. An urgent need therefore exists for a liquid-sensitive actuator which will respond rapidly upon immersion in a liquid, especially for use in flotation devices designed to preserve life, yet will not prematurely actuate such devices by responding to damp atmospheric conditions, even over extended periods.